DarkRadiant
From The DarkMod Wiki
DarkRadiant is The Dark Mod's very own map editor, based on the open-source GTKRadiant.
Orbweaver started working on it in Spring 2006, the initial release was version 0.5.0. Features at this stage include a categorised entity inspector, drag-resizable lights, color selection tool for lights and numerous bugfixes over the GtkRadiant codebase.
DarkRadiant - Quick Installation Guide
